Royal Enfield 350 BULLET 1949, Workshop Maintenance Manual, Page: 17 / 102

ROYAL ENFIELD WORKSHOP MANUAL
marked the pin so that it, and the piston, may be
replaced the same way round, i.e. split skirt to the
front.
During this operation put a piece of clean rag
in the top of the crankcase to prevent foreign
matter getting in. In particular, take care not to
drop the circlip in the crankcase.
12. Decarbonising
Having removed the cylinder head as
described in Subsection 6, scrape away all carbon,
bearing in mind that you are dealing with
aluminium which is easily damaged. Scrape
gently to avoid scoring the combustion chamber
or the valve seats, which are of austenitic iron
shrunk into the head. Be careful not to injure the
joint face which beds down on to the head gasket.
Do not, in any circumstances, use caustic
soda or potash for the removal of carbon from
aluminium alloy.
Scrape away all carbon from the valve heads
and beneath the heads, being careful not to cause
any damage to the valve faces.
If the piston rings are removed, the grooves
can be cleaned out and new ones fitted. For
cleaning the grooves a suitable tool is a piece of
broken ring thrust into a wooden handle and filed
to a chisel point.
While the cylinder and piston are not in
position, cover the crankcase with a clean cloth
to prevent the ingress of dust and dirt of all
kinds. Do not, of course, attempt to scrape the
carbon from the piston when the mouth of the
crankcase is open.
13. Grinding in the Valves
Wipe the valve faces clean and examine them
carefully. If they are at all pitted, have the faces
recut. Pay similar attention to the valve seats in
the head; excessive grinding will form a pocket
and the gas flow will be restricted. The angle of
the valve face should be 45 degrees to the axis of
the valve stem.
To grind a valve, smear the seating with a
little grinding in compound, place a light, short
coil spring over the valve stem and beneath the
head, insert the valve into its appropriate guide,
press it on to the seat, using a tool with a suction
cup and with a backwards and forwards rotary
motion, grind it on to its seat. Alternatively, use a
tool which grips the valve stem and pulls the
valve on to its seat. Frequently lift the valve and
move it round so that an even and true seating is
obtained. Continue grinding until a bright ring is
visible on both valve and seating.
14. Reassembly after Decarbonising
Before building up the engine, see that all
parts are scrupulously clean and place them
conveniently to hand on a clean sheet of brown
paper.
When reassembling the engine, it is advisable
to fit a new paper washer between the cylinder
barrel and the crankcase.
Smear clean oil over the piston and space the
ring gaps, having replaced the rings if these have
been removed. The taper ring is marked "TOP"
on the upper face. Lower the piston over the
connecting rod and insert the gudgeon pin. Fit the
circlip securing the gudgeon pin.
If the piston ring gaps exceed 1/16 in. when
the rings are in position in the barrel, new rings
should be fitted. The correct gap for new rings is
between .011 in. and .015 in. The gap should be
measured in the least worn part of the cylinder,
which will be found to be the extreme top or
bottom of the bore.
Oil the cylinder bore and lower the barrel over
the piston and seat it gently on the paper washer.
Tighten down the nut above the tappet chest and
replace the cylinder head and rockers as
described in Subsection 4.
15. Cleaning the Oil Filter
The oil filter is located in the timing cover
immediately below the oil pumps. The felt
element should be taken out and washed in petrol
after the first 500 miles and every subsequent
2,000 miles. Fit a new element every 5,000 miles.
Section C2 Page 4
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